With acoustic systems and in particular with hearing devices, it is advantageous to combine a number of microphone signals and filter them spatially and spectrally so that the output signal contains as few interference components as possible. Interference here is defined on the one hand as signals, which are incident from unwanted directions, for example outside a predetermined angle range around the 0° direction, and on the other hand as microphone noise, which is amplified in low-frequency ranges in particular when establishing the directivity. The problem arises in particular that microphone noise increases, when the directivity of a directional microphone is enhanced.
In DE 10 2004 052 912 A1 an acoustic system and a method are specified, which suppress interference power in directional microphones as far as possible. To this end the microphone signals of a number of microphones are filtered adaptively as a function of at least one parameter. The directivity of the directional microphone thus obtained is adjusted by changing the at least one parameter so that the sum of interference power including microphone noise is reduced or minimal. There is therefore a switch between directional operation and omnidirectional operation depending on noise distribution.
The method described in DE 10 2004 062 912 A1 results in minimization of the total power made up of microphone noise and ambient noise. Half of residual noise consists of residual ambient noise and half of residual microphone noise. Mathematically speaking the overall interference is minimal, but not for the subjective sound impression of a user of the acoustic system. Rapidly changing signal components and broad partial band signals mean that disruptive microphone noise is repeatedly perceptible for the user. Non-stationary interferers in particular, such as speech, cause a brief switch to directional operation. If the interferer then becomes inactive again, there is a delayed switch to omnidirectional operation, so that noise tails are briefly audible.